[R6RS] Fresh syntax

[dyb at cs.indiana.edu]

> >  (define-syntax main
> >    (lambda (stx)
> >      (let ((make-swap
> >             (lambda (x y)
> >               (with-syntax ((x x) (y y))
> >                 (fresh-syntax
> >                   (let ((t x))
> >                     (set! x y)
> >                     (set! y t)))))))
> >        (syntax-case stx ()
> >          ((_)
> >           (with-syntax ((swap (make-swap (syntax s) (syntax t))))
> >             (syntax
> >               (let ((s 1) (t 2))
> >                 swap
> >                 (list s t)))))))))

> I wasn't able to write a correct equivalent of the above example using 
> make-syntax-introducer.  If fresh-syntax works as above, then I think 
> I'm satisfied (for now!), except that FRESH-SYNTAX isn't yet part of the 
> proposal.

I've just committed a new version of the reference implementation that
supports fresh-syntax, and the example above works as expected.  I have
not moved fresh-syntax from the issues section into the main body of the
SRFI document but will do so if two or more of you speaks up for it. 
(I'll count Anton as one already, so one more is enough.) For my part, I
don't see a compelling need for this feature but nor do I object to
including it.

Kent